The present invention generally relates to the field of preparation methods of dye dispersions and to elements, more particularly in the field of silver halide photography, comprising said dye dispersions in an antihalation or safelight protection layer.
The photographic industry has since quite a long time recognized the need to provide photographic elements with some form of antihalation protection. Halation has been a persistent problem occurring with photographic films comprising one or more photosensitive silver halide layer(s) coated on a transparent support. The emulsion layer diffusely transmits light which then reflects back into the emulsion layer from the support surface. The silver halide emulsion is thereby re-exposed at locations differing from the original light path through the emulsion, which results in xe2x80x9chalo-ringxe2x80x9d formation on the film surrounding images of bright objects.
Another problem more particularly encountered e.g. with motion picture print films is exposure of silver halide light-sensitive layers by safelights along the support through xe2x80x9clight-pipingxe2x80x9d. Commonly used safelight in motion picture industry emits radiation in the range of 560-630 nm, and therefore e.g. a Kodak Safelight Filter No.8 is useful. This means that in particular for the red sensitive layer of the motion picture print film a safelight protection is required.
In order to provide antihalation protection in photographic films one method makes use therefor of a dyed or pigmented layer behind a clear support as an antihalation backing layer, wherein the said backing layer is designed to be removed during processing of the film. Typical examples of such antihalation backing layers comprise a light absorbing dye or pigment (such as carbon black) dispersed in an alkali-soluble polymeric binder (such as cellulose acetate hexahydrophthalate) which makes the layers be removable by an alkaline photographic processing solution. Such carbon containing xe2x80x9crem-jetxe2x80x9d backing layers have been commonly used for antihalation protection in motion picture films. Moreover such a backing layer provides in a very efficient safelight protection of the light sensitive layers.
While such xe2x80x9crem-jetxe2x80x9d backing layer provides effective antihalaton and safelight protection for photographic films prior to processing, use of it requires special additional processing steps in order to provide subsequent complete removal as incomplete removal of carbon particles may cause image defects in the resulting exposed print film when viewing on a screen during projection.
Accordingly an alternative layer arrangement or layer built-up for backing layers of elements containing carbon particles as pigments providing antihalation/safelight protection, said layers being removable in the processing of the said elements, is highly desirable.
One such alternative makes use of antihalation undercoat layers containing filter dyes coated between the support and the light-sensitive emulsion layers wherein the said filter dyes are solubilized and removed and/or decolorized during the processing of the film as has e.g. been illustrated in EP-A""s 0 252 550 and 0 582 000, as well as in EP-A""s 0 456 163, 0 587 229, 0 587 230, 0 656 401, 0 724 191, 0 786 497 and 0 781 816 and in U.S. Pat. Nos. 4,394,441; 4,900,652; 4,994,355; 5,223,382; 5,278,037; 5,232,825; 5,326,686; 5,346,810; 5,460,916; 5,462,832; 5,491,058; 5,700,630; 5,709,983; 5,723,272; 5,744,292; 5,928,849; 5,786,134; 5,866,309; 5,952,163 and 6,027,866. Dyes may be incorporated in layers as sole selected dyes or in combinations of dyes in order to provide antihalation protection throughout the whole visible spectrum, as e.g. for black-and-white microfilms. More particularly protection over almost the whole visible wavelength spectrum (400-750 nm) is desired for motion picture print films since these materials are sensitive to radiation covering the said spectrum.
With respect to safelight protection, more particularly in the range from 560 to 630 nm, the extinction of the dyes should be high enough in order to provide an absorption density preventing the red-sensitive layer to be exposed by safelight through the support. Useful dye combinations therefor can be found more particularly in in EP-A""s 0 656 401, 0 724 191, 0 756 201, 0 781 816 and 0 786 497.
In order to obtain efficient antihalation and safelight protection over the whole visible wavelength range combinations of different dyes should also provide extinctions which should be high enough in order to provide high enough an absorption density over the said range. This means that substantial amounts of dyes are required in the antihalation layers. Since it is very important to reduce the load (and thickness) of the layers from a point of view of manufacturing costs of the photographic element as well as from the point of view of decolorizing properties in the processing, more particularly in rapid processing cycles, it is of crucial importance to choose the most efficient combination of dyes and the best way possible in order to combine them before adding them to coating solutions for the designed layers wherein they are preferred.
It is an object of this invention to provide antihalation/safelight protection layers wherein dyes are present, selected and combined in such a way that low amounts of said dyes having excellent extinction properties and light-absorption properties over the desired wavelenght range become available in order to provide enough absorption density over the whole desired range, thus providing protection of the photosensitive layers and the material against safelight and reflection by the support.
In order to reach the objects of the present invention a method for preparing a co-precipitated microcrystalline dye dispersion has thus been obtained, the absorption spectrum of which exceeds the summoned spectra of the individually dispersed dyes, which comprises as consecutive steps
adding to one (a first) vessel, an amount of at least one pentamethine oxonol-type barbituric acid filter dye having ionizable sites in its molecular structure;
adding thereto an aqueous alkaline solution in an amount sufficient to completely dissolve the said filter dye while stirring the solution thus formed;
adding in another vessel, to an amount of at least one pyrrole type dye, an amount of water, followed by addition of an aqueous alkaline solution and a surfactant and, after having completely dissolved the said pyrrole type dye,
adding, while further stirring, to the solution of the pyrrole type dye(s), the solution of the pentamethine oxonol-type barbituric acid dye(s);
adding an aqueous acidic solution up to a pH of less than 3.0;
adding an aqueous alkaline solution up to a pH in the range from 4.0 up to 5.5; and
adding a binder.
According to the present invention incorporation of the thus obtained co-dispersion(s) in dye antihalation or safelight protection layers of light-sensitive silver halide photographic elements or materials in order to provide particularly suitable antihalation characteristics or safelight protection as a backing layer of said material, or as layer covering the light-sensitive layer.